1. Field of the Invention
The present invention relates generally to a synchronous mobile communication system (e.g., cdmaOne, cdma2000 1x), and more particularly to a method and apparatus for increasing the battery waiting time of a User Equipment (UE) through an efficient processing of assigned slots.
2. Description of the Related Art
In a synchronous mobile communication system, a UE generally searches a paging channel and receives and processes paging and control information while in a waiting state. In this case, the UE operates in either a slotted or non-slotted mode. In the slotted mode, an entire paging channel is divided into 80 ms slots, and a UE searches only a slot promised between the UE and node B. In the non-slotted mode, all slots are searched. A slot includes 4 frames, each of which has a data processing unit of 20 ms. When the mobile communication system operates in the slotted mode, the UE transits into an active state and searches a paging channel only during assigned slots, and enters a sleep state without searching a paging channel during non-assigned slots. During the sleep state, the operations of a Radio Frequency (RF) modem, a Central Processing Unit (CPU) and other hardware devices are stopped, thereby reducing battery power consumption.
In this case, the node B and UE may calculate a promised slot by using the following Equation (1).(└t/4┘−PGSLOT)mod(16×2i)=0   (1)
In Equation 1, “t” represents a system time with a unit of 20 ms, “PGSLOT” represents a value commonly known by the node B and the UE through the unique telephone number of the UE and has a value within a range of 0 to 2047 according to UEs. In addition, “i” refers to a slot cycle index representing a paging channel searching period, and has a value within a range of 0 to 7. As the value of the slot cycle index increases, the paging channel searching period increases, so that a time period during which the UE stays in the sleep state is also extended. For example, when “i” has a value of “0,” an assigned slot is searched once every 1.28 seconds, and when “i” has a value of “2,” the assigned slot is searched once every 5.12 seconds. During the waiting state, the UE generally operates in the slotted mode.
The cases in which the UE operates in the non-slotted mode will now be described with reference to the fields of a paging message shown in FIG. 2.
1. When control information changes (i.e., when current control information which the UE has is unavailable), the UE operates in the non-slotted mode.
The control information includes node B configuration information and access parameter information. When the node B configuration information changes, it can be recognized by checking a CONFIG_MSG_SEQ field included in the node B configuration message and a page message. Since the UE must again receive all node B configuration messages when the node B configuration information changes, the UE operates in the non-slotted mode so as to update the node B configuration information as soon as possible. Also, when access parameter information changes, it can be recognized by checking an ACC_MSG_SEQ field included in an access parameter message and a page message. Similarly, when the access parameter information changes, the UE operates in the non-slotted mode so as to update the access parameter information.
2. When the UE transmits a message to the node B through an access channel “ACH” and waits for an acknowledgement of the message, the UE operates in the non-slotted mode.
Since message transmission through an access channel is performed through connectionless communication without a logical path for connection to the node B, it is necessary for the UE to receive delivery confirmation. In this case, although an assigned slot has passed, the UE must not enter the sleep state before receiving a response to the message.
3. The UE operates in the non-slotted mode when it is established to do so.
In cases other than the above three cases, the UE may also enter the slotted mode so as to save power. FIG. 1 illustrates the configuration of a slot in a conventional mobile communication system, in which slot various types of messages are arranged according to a predetermined rule. In FIG. 1, a paging channel is shown having a unit of 20 ms frame in which the configuration of an assigned slot is shown.
In the paging channel, mobile addressed messages, such as an Order Message (ORDM) and an Enhanced Channel Assignment Message (ECAM), to be transmitted from node B to a specific UE are generally positioned at the front portion of the paging channel. When there is no message to be transmitted from the node B to the UE, the corresponding portion is empty. In the portion following the front portion, a General Page Message (GPM) used when the node B pages a specific UE is inserted, and the remaining portions of the slot are filled with an OVerHeaD message (OVHD) containing configuration and access information, which are commonly transmitted to all UEs registered in the node B. FIG. 1 shows the earliest point at which a UE can transit into a sleep state in an assigned slot.
When operating in the slotted mode, the UE searches an assigned slot. When it is determined that there is no paging information related to the UE, and configuration information stored in the UE is available, the UE enters the sleep state. In contrast, when there is paging information during the assigned slot, or when configuration information changes, the UE must perform an operation necessary for call connection or receive changed configuration information, without entering the sleep state. However, in this case, it is unnecessary for the UE to search all of the assigned slot. This is because when checking only a part of the contents of a paging message initially received in an assigned slot, the UE may enter the sleep state without checking the contents of the following messages in the assigned slot.
For example, in cdma2000 1x, a General Page Message (GPM) contains: a CONFIG_MSG_SEQ field representing whether node B configuration information changes; an ACC_MSG_REQ field representing whether access parameter information changes; CLASS_0_DONE field, CLASS_1_DONE field, TMSI_DONE field, and a BROADCAST_DONE field (hereinafter DONE fields), that represent whether a page message for each group, to which UEs belong, exists in a slot assigned according to each corresponding group; and a PAGE_RECORD field representing the unique number of an actually paged UE. Among these fields, when the value of the CONFIG_MSG_SEQ field or of the ACC_MSG_REQ field changes to a value other than that stored in the UE, it is necessary to update the node B configuration information or access parameter information.
Herein, through the DONE fields registered in the UE, the UE can determine whether it is necessary to receive a message following a currently received general page message. For example, when a DONE field has a value of “1,” the UE does not need to receive a following message in an assigned slot, but when the DONE field has a value of “0,” the UE must continuously receive the following message. That is, after checking the fields of the general page message, when the UE determines that there is no configuration information and/or access information to be updated, and it is unnecessary to check the following messages, the UE may transit into the sleep state. Although the above description is given in terms of processing a general page message in the cdma2000 1x system, the operations may be applied to the cdmaOne system in such a manner as to check the fields of a Page Message (PM).
As described above, a. UE being in the slotted mode can transit into the sleep state so as to save power.
Since the UE usually operates in the slotted mode, power consumption decreases as the UE transits faster into the sleep state. Therefore, a rapid sleep state entry method is required.
FIG. 3 illustrates a conventional paging channel processing operation in which a UE starts to operate at a slot boundary, receives and processes a message, and then transits into the sleep state.
A roll boundary represents the starting point of a short PN code having a 26.666 ms period, which is used in a synchronous mobile communication system.
When the UE is in the sleep state, the state of the PN code is not updated. In this case, since the state of the PN code of the node B is being continuously updated, the UE must perform an operation to adjust the state of its own PN code to match that of the node B when the UE wakes up from the sleep state. To this end, the prior art is designed to enable sleep state entry and active state entry only at the roll boundary.
Meanwhile, the UE decodes paging channel data by generally using a Viterbi decoder (not shown). The Viterbi decoder reports a result of decoding to a processor through interrupt every 20 ms on the basis of a slot boundary. Herein, the “processor” may be a typical processing unit of the UE, an application of a controller, or software.
Therefore, as shown in FIG. 3, a conventional UE processing a paging channel at an active state causes a decoding delay due to the Viterbi decoder. That is, when an interrupt of 20 ms occurs, data reported from the decoder to the processor includes portions of a previous frame and portions of a current frame, because the conventional paging channel processing method processes paging channel data in a unit of 20 ms frame.
Consequently, in order for the UE to enter the sleep state, the Viterbi decoder must wait until the second decoder interrupt #2 occurs so that the processor can process data of the first frame in an assigned slot, and then the UE can enter the sleep state at the second roll boundary.
That is, data #1 obtained from decoder interrupt #1 of the first frame and a portion of data #2 obtained from decoder interrupt #2 of the second frame due to the decoding delay are processed in units of 20 ms frames, and then it is determined based on a result of the processed data whether to enter the sleep state.
In this case, the processor must actually wait for 40 ms after a slot starts, before the processor performs the first processing operation with respect to paging channel data.
When the first frame data includes a general page message which has no paging and control information to be updated, the UE can transit into the sleep state at a roll boundary after the first frame data. In contrast, when the above conditions are not satisfied, the second frame must be used to determine whether to transit into the sleep state, so that an actual transition into the sleep state is further delayed.
As described above, according to the conventional procedure of starting at a slot boundary, receiving and processing a message, and performing a transition operation into the sleep state, there is a problem in that the earliest the UE can transit into the sleep state is at the second roll boundary.
This results in a delay in the sleep-state transition time point of the UE, thereby unnecessarily extending the time during which an RF receiver is in an on-state.
Therefore, it is necessary to develop an efficient sleep-state entry method considering such a decoding delay.